Receiving apparatus for communication systems



Dec. 14, 1937. w. P. PLACE 2,102,435

I RECEIVING APPARATUS FOR COMMUNICATION SYSTEMS Filed March 26, 1957Amplifiew Demodulaiop. BF? f f .7 ll 7 6 7 W1:

. INVENTOR T Vllllcr P6009;

HIS ATTORNEY the system is in working order.

Patented Dec. 14, 1937 PATENT oreicn RECEIVING APPARATUS FOR COMMUNI-CATION SYSTEMS I Willard P. ,Elace, Wilkinsburg, Pa., assignor to TheUnion Switch & Signal Company, Swissvale, Pa., a corporation ofPennsylvania Application March 26,

12 Claims.

My invention relates to receiving apparatus for communication systems,and particularly to receiving apparatus for communication systemsoperating on the closed circuit principler I shall describe one form ofapparatus embodying my invention, and shall then point out the novelfeatures thereof in claims.

A feature of my invention is the provision of novel and improvedreceiving apparatus for communication systems which operate on theclosed circuit principle by virtue of a signaling current of apredetermined characteristic normally flowing in the transmittingcircuit for continuously indicating during non-communicating periodsthatv Other features and advantages of my invention will appear as thespecification progresses.

Receiving apparatus constructed in accordance with my invention isnormally conditioned for reception and is responsive to signalingcurrent of a predetermined frequency for actuating an indicator, and theapparatus is automatically conditioned for reproducing the voicefrequencies of a telephone current when such signaling current ceases.Discontinuance of the display of the indicator when not immediatelyfollowed by reception of a telephone message is a warning of a failureof the system.

Apparatus embodying my invention is especially useful for communicationsystems for railway trains where the movements of a train are governedin part, at least, in accordance with verbal instructions receivedaboard a vehicle of the train from a remote station, the communicationcurrent being transferred to such vehicle through the mediurn of traincarried elements effectively coupled With wayside circuits. Preferably,the communication current is picked up by the train carried apparatus byvirtue of an inductor mounted on a vehicle of the train in inductiverelation with the track rails, the track rails being included in awayside transmitting circuit. It will be understood, however, that myinvention is not limited in its use to communication systems for railwaytrains, and many places will suggest themselves Where the apparatus willbe 1937, Serial No. 133,214

is disposed for inductive relationship with a transmitting circuit, notshown. When the apparatus is installed on a vehicle of a railway train,the inductor coil 10 preferably is mounted on the vehicle in inductiverelation with the track rails. The electromotive forces induced in theinductor coil IC in response to current flowing in theassociatedtransmitting circuit are applied over wires 2 and 3 to the input side ofthe filter BPF, the output side of which filter is connected over wires5 and 6 with the input terminals of the amplifier-demodulator AD. Acircuit controlling contact 4, to be referred to later, may beinterposed in the wire 3. The filter BPF is of the usual band-pass typeand is proportioned and adjusted to pass the frequency band of thecommunication current and to substantially suppress frequencies eitherabove or below such band. For example, it has been proposed incommunication systems for railway trains to employ the upper side bandof a carrier current of 7000 cycles per second modulated with voicefrequencies for telephone communication, and to use the equivalent ofsuch carrier current modulated by a single predetermined voice frequencyfor signaling. Under such circumstances, the filter BPF would pass aband extending from 7500 to 9500 cycles, the voice frequency range beingtaken as extending from 500 cycles to 2500 cycles. For signaling, thecurrent may be that of 7800 cycles, which is the equivalent of the uppersideband of the carrier of 7000 cycles modulated by the voice frequencyof 800 cycles.

The amplifier-demodulator AD may be any one of several Well-known typesfor such devices, and I is shown conventionally only for the sake ofsimplicity. It is deemed sufficient for this application to point outthat the amplifier-demodulator AD includes a normally active source ofcarrier current for mixing with the incoming communication current, andis operative to cause only the voice frequencies to appear in the outputcircuit of the demodulator, the local carrier and the other products ofdemodulation being suppressed and not appearing in the output circuit.On the assumption the communication current is of the frequenciesreferred to hereinbefore, then the ,voice band of frequencies extendingfrom 500 to 2500 cycles per second would appear in the output circuit ofthe demodulator when telephone current is picked up by the inductor coilIC, and the single predetermined frequency of 800 cycles per secondwould appear in the output circuit when signaling current is picked upby the inductor coil IC.

The amplifier-demodulator AD is provided with a normally closed outputcircuit including a resonant circuit and a winding operativelyassociated with a loud speaker or telephone receiver. As here shown, theresonant circuit is of.

the parallel resonant circuit type consisting of an terminal of theresonant circuit is connected over V I output circuit is not large atthe voice band of frewire 1 with one output terminal of theamplifierdemodulator AD, and a mid terminal of the inductorL isconnected'over wire l0, voice coil 9 of loud speaker LS and wire 8 withthe other output terminal of the amplifier-demodulator. The res-v onantcircuit consisting of, inductor L and condenser vCL is proportioned forresonance'at the voice frequency corresponding to the predeter minedfrequency of the signaling current. When;

the 'slgnaling current is of the frequency assumed hereinbefore for thepurpose of illustration, the resonant circuit is tuned for resonance'at800 cycles per-second. Consequently, a. currentof relatively largeamplitude-of 800 cycles persecond flows in the output'circuit inresponse to the signaling current picked up by the inductor coil 10 andsupplied to the amplifier-demodulator The parts are further soproportioned "and the :terminal of inductor L, to which wire 10 isconnected, is so positioned that the impedance of the quencies, and thewinding 9 is effectively.infiu-. enced when the telephone current ispicked up by the inductor coil IC and supplied to the amplifler-demodulator. 7

n A portion of the winding of inductor L is connected across-the inputterminals ,of a full wave rectifierv H, the output te'rminalsof whichare connected with-the winding 12 of arelay R. It follows that the relayR is effectively energized by rectified current and pickedup in responseto the signaling current flowing in the output circuit of theamplifier-demodulator, but that the relay is deenergized and immediatelyreleases when the signaling current ceases.

The relay R controls a first indicator here shown in the form of a lampB, a second indicator here shown in the form of a bell l4, and, thefield winding l5'of the loud speaker LS. The indication lamp I3 isilluminated bycurrent supplied over a simple circuit including the Bterminal of any convenient source of current such as a battery not 'pickup of relay R, the circuit being closed during the interval the backcontact I! and the front contact 20 are both in engagement with thetransfer contact I 8, as will be readily understood by an inspection ofthe drawing. 7

The operation of the'app'aratus is as' follows. 7

Under normal conditions, that is, during non-telephone periods,signaling current is continuously supplied to the transmitting circuitby apparatus at an associated remote station, and the electromotiveforce induced in theinductor coil IC is of the frequency correspondingto the frequency of the signaling current. This frequency of theelectromotive'force falls within the pass band of the filter BPF, andhence the electromotive force is demodulator, and which latter frequencyis the resonant frequency of the resonant circuit consisting of inductorL and condenser CL. Consequently, during reception of-signaling currentthe relay R is effectively energized and picked up by the rectifiedportion of current passed by the.

rectifier ll. With the relay, R picked up to close front contact 16, thelamp I3 is illuminated to indicate the receptionbf signaling current. Inother words, the lamp [3, when illuminated, indicates that thetransmitting circuit and the receiv ing apparatus are in working order.7

i When the signaling current is interrupted, the relay R is deenergizedand at'once releases, the lamp I3 being extinguished when the front'contact I6 is opened. During the release of relay R, the bell I4. issounded when both the back contact Hand the front contact 20 are inengagement with the transfer contact l8, and'the belllaudibly'indicatesthe termination of the signaling current;' With the relay Rfully-released; to close back contact lfl, the field winding I5 of theloud speaker L8 is energized and the loud V speaker is conditioned forreproductionof the voice frequencies of va current flowing in the voicecoil 9. The electromotive forces inducedin' the inductor coil 1G by atelephone current flow ing in the transmitting circuit are passed by thefilter BPF' to; the amplifier-demodulator and;

cause corresponding voice frequencies to 1 appear in the output circuitof thedemodulato'r, with the result that the telephone message isreproducedby the loud speaker 'LS. At

the termination of telephone communication,

the restoring of the apparatus to the normal condition. If no speechfollows the extinction of the lamp I 3, then the operator would knowthat the system is out of order and may take- 7 Whatever steps arenecessarysi A portion of the winding [2 of relay R is short-circuitedover a back contact 2| of the relay and the relay is provided with slowpick-up characteristics. Therelay R is preferably slow to pick up sothat occasional current of the predetermined voice frequency of thesignaling current which may pass through the rectifier to the relay Rduring reception of telephone current does not energize the relay for asuflicient period to pick up the relay and interrupt the operation ofthe loud speaker.

7 It is to be understood that receiving apparatus and transmittingapparatus may-be provided at the same station and two-way communicationmay be carried on. It is understood, of course, that thetransmittingapparatus at one station does not interfere with the operation of J thereceiving, apparatus at the same station. This implies differentfrequencies, different paths for r the transmitted and receivedcurrents, or any other suitable well-known means. As 'here shown, thecontact 4 would be operated either" Although specific frequencies havebeen used in illustrating the invention, it will be understood that theinvention is not limited to these frequencies and other frequencies forthe communication current may be selected if desired. As a matter offact, the frequency of the signaling current may be outside of the voiceband.

In the foregoing description, I have referred to the signaling currentas being used primarily to check that the system is in Working order. Itis clear that the signaling current may also be used for code signalingby providing apparatus at the remote station effective to periodicallyinterrupt the signaling current in accordance with a prearranged code.Under such circumstances, the relay R and the indicators l3 and I wouldbe operated in accordance with the prearranged code.

Although I have herein shown and described only one form of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Receiving apparatus for communication systems comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to the carrier modulated by a predeterminedfrequency, a parallel resonant circuit proportioned for resonance atsaid predetermined frequency, a loud speaker, a first winding associatedwith the loud speaker, means to connect said resonant circuit and saidfirst winding across the output terminals of the demodulator to form anoutput circuit for the demodulator, a relay, means to connect a windingof the relay with said resonant circuit to energize the relay inresponse to such signaling current supplied to the demodulator, andcircuit means including a back contact of the relay and a second windingassociated with the loud speaker as well as a current source tocondition the loud speaker as required for reproducing the voicefrequencies of the current flowing in said first Winding in response tosuch telephone current supplied to the demodulator.

2. Receiving apparatus for communication systems comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to the carrier modulated by a predeterminedfrequency, a parallel resonant circuit proportioned for resonance atsaid predetermined frequency, a loud speaker, a first winding associatedwith the loud speaker, means to connect said resonant circuit and saidfirst winding across the output terminals of the demodulator to form anoutput circuit for the demodulator, a relay, means to connect a windingof the relay with said resonant circuit to energize the relay inresponse to said signaling current supplied to the demodulator, anindication circuit including an indicator and a front contact of therelay to indicate the reception of signaling current, and other circuitmeans; including a back contact of the relay and a second windingassociated with the loud speaker to condition the loud speaker asrequired for reproducing the voice frequencies of the current flowing insaid first winding in response to said telephone current supplied to thedemodulator.

3. Receiving apparatus for communication systems comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to the carrier modulated by a predeterminedfrequency, a parallel resonant circuit proportioned for resonance atsaid predetermined frequency, a loud speaker, a first winding associatedwith the loud speaker, means to connect'said resonant circuit and saidfirst winding across the output terminals of the demodulator to form anoutput circuit for the demodulator, a relay, means to connect a windingof the relay with said resonant circuit to energize the relay inresponse to said signaling current supplied to the demodulator, anindication circuit including a lamp and a front contact of the relay toindicate the reception of signaling current, another indication circuitincluding a bell and a contact closed momentarily when the relay isreleased to indicate when reception of the signaling current ceases, andother circuit means including a back contact of the relay and a fieldwinding of the loud speaker to condition the loud speaker forreproducing the voice frequencies of the current flowing in said firstwinding in response to reception of said telephone current.

4. Receiving apparatus for communication systems comp-rising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to the carrier modulated by a predeterminedfrequency, a parallel resonant circuit including an inductor and acondenser and proportioned for resonance at said predeterminedfrequency, a loud speaker provided with a voice winding and a fieldwinding, means to connect said resonant circuit and said voice windingin series across the output terminals of the demodulators to form aclosed output circuit for the demodulator, a relay, means including arectifier to connect a winding of the relay across a portion of saidinductor to energize the relay as long as such signaling current issupplied to the demodulator, an indication circuit including anindicator and a front contact of the relay, and circuit means includingsaid field winding and a back contact of the relay to condition the loudspeaker for reproducing the speech of such telephone current supplied tothe demodulator.

5. In combination, receiving equipment normally conditioned forreception of a signaling current of a predetermined single frequency ora telephone current of the voice frequency range, a resonant circuitincluding an inductor and a condenser and proportioned for resonance atsaid predetermined frequency, a loud speaker provided with a voicewinding and a field winding, means for connecting said resonant circuitand said voice winding in series across the output terminals of saidreceiving equipment to form a closed output circuit, a relay, meansincluding a rectifier to connect a winding of the relay across a portionof the inductor to energize the relay when current resulting fromreception of the signaling current fiows in the output circuit, anindication circuit including an indicator and a front contact of therelay to indicate reception of signaling current, and circuit meansincluding said field winding and a back contact of the relay tocondition the loud speaker when the signaling current ceases forreproducing the voice frequencies of the current flowing in the outputcircuit as a result of reception of the telephone current.

6. In combination, receiving equipment normally conditioned forreception of a signaling current of a predetermined single frequency ora telephone current of the voice frequency range, a resonant circuitincluding an inductor and a r current flows in the output circuit, anindication predetermined frequency, a loud speaker, provided I with avoice winding and a field winding, means for connecting said resonantcircuit and said voice 7 winding in series across the output terminals.of said receiving equipment to form a closedoutput circuit, a relay,means including a rectifier to connect a winding of the relaytacross aportion of the inductor to energize the relay when current resultingfrom reception of the signaling circuit including an indicator andafront contact of therelay to indicate reception of signaling current,circuit means including said field winding and a back contact of therelay to condition the loud speaker when the signaling current ceasesfor reproducing the voice frequencies of the current flowing in-theoutput circuit'as a result of reception of the telephone current, andmeans terminal of the tuned circuitwith one output terminal of saidreceiving equipment and to conmeet a mid terminal of the inductor withthe other output terminal of the receiving equipment over said windingto form a closed output circuit for the receiving equipment, a relay,means including a rectifier to connect a winding of the relay acrossa'portion" of said inductor to energize-said relay when currentresulting from reception oisaid signaling current flows 'in'said outputcircuit, an indicator circuit controlled by said relay when energized toindicate reception of signaling current, and circuit means controlled bysaid relay when deenergized to condition said loud speaker as requiredfor actuation of the "loud speaker by the first mentioned Winding whencurrent resulting from reception of said telephone 7 current flows insaidoutput circuit.

8. Receiving apparatus for communication systerns comprising, ademodulator capable of demodulating a carrier telephone current and asignaling current equivalent to the carrier modulated by a predeterminedfrequency, a loud speaker provided with a voice coil and a field coil, atuned circuit consisting of an inductor and a condenser and tuned toresonance at said predetermined frequency,'an output circuit connectedwith the output terminals of said demodulator and including said tunedcircuit and said voice coil, a relay, means toconnect a windingof therelay across a portion of said inductor to energize the relaywhen'current of said predetermined frequency fiows in said'outputcircuit, an indication circuit including a front con tact of therelay and an indicator as wellas'a current source to display anindication as long as such signaling current is supplied to thedemodulaton'and another circuit including a back contact of the relayand said field coil as well as a current source to render the loudspeaker responsive to the voice frequencies of current fiowing in saidoutput circuit when the signaling current ceases and said telephonecurrent is supplied to the demodulator.

9. Receiving apparatus for communication sys-' tems comprising, ademodulator capable of :de- 7 modulating a carrier telephone current anda sig-, 7

naling current equivalent to the carrier modulated by' a predeterminedfrequency, a loud speaker, a

tuned circuit consisting of an inductor'and a condenser and tuned toresonance at said predetermined frequency, an, output circuit connectedwith the output terminals of said demodulator and including said tuned,circuit and a first winding associated withthe loud speaker in series, arelay,

means to connect a winding of the relay across a portion of saidinductor to energize the relay signaling current ceases for reproductionofythe voice frequencies of the current flowing in said first windinginrresponse to telephone current supplied to the demodulator. V r V 10;"Receiving apparatus for communication systems comprising, a demodulatorcapable of: demodulating a carrier telephone current and" a signalingcurrent equivalent to the carrier -modulated by a predeterminedfrequency, a loud speaker, a tuned circuit consisting of an inductor 30and a'condenser and tuned to resonance at said predetermined frequency,an output circuit connectedrwith the output terminals of said demod- Vulator and including said tuned circuit and a first winding associatedwith the loud speaker in series a' relay, meansto connect a winding ofthe relay across a portion of said inductor to 7 energize the relay whencurrent of said predea termined frequency flows in said output circuit 7in'response to signaling current supplied tothe demodulator, anindication circuit including an indicator and a front contact of saidrelay to display an indication as long as signalingcurrent is suppliedto the demodulator, and other circuit means including a back contact ofthe relay and. t

a second winding associated withthe loud speaker to condition theloudspeaker when such signaling ceases for reproduction of the'voicefrequencies of currentfiowing in'said first winding in response 'to saidtelephone currentsupplied' to the demodulator. 7

11. In combination, receiving equipment normally conditioned forreception of communication current and including a demodulator capableof demodulating a given. telephone current and a signaling current of apredetermined frequency,

a normally closed output circuit connected with said demodulator andincluding an inductor and a condenser arranged in parallel and in serieswith another winding, said inductor and condenserprcportioned forresonance at the frequency corresponding to said. signaling current whendemodulated, a loud speaker operatively associated with'said otherwinding but normally inactive, a relay, means including a rectifier toconnect'awinding of, the relay across a portion of said inductor toenergize the relay as long as signaling current is received, indicationmeans 7 controlled by saidrelay' to indicate reception of the signalingcurrent; and other means controlled I 7 by said relay'to render saidloud speaker active and effective only'when said relay isdeenergized.

V 12. In combination, receiving equipment nor-f mally conditioned forreception of communication current and including a demodulator capableof demodulating a given telephone current and a signaling current of apredetermined frequency, a normally closed output circuit connected withsaid demodulator and. including an inductor and a condenser arranged inparallel and in series with another Winding, said inductor and condenserproportioned for resonance at the frequency corresponding to saidsignaling current when demodulated, a loud speaker operativelyassociated with said other winding but normally inactive, a relay, meansincluding a rectifier to connect a winding of the relay across a portionof said inductor to energize the relay as long as signaling current isreceived, indication means controlled by said relay and including a lampto visually indicate reception of the signaling current and a bell tosound a warning when the signaling current ceases, and other meanscontrolled by said relay to render said loud speaker active andeffective only when the relay is released.

WILLARD P. PLACE.v

